366 
POPULAR SCIENCE REVIEW. 
It is obvious that the accurate determination of the causes of 
the changes above alluded to is a point not only of high physio- 
logical interest, but also of much practical value. A working 
gardener is often puzzled, and his employer disgusted, at find- 
ing his strawberries barren, his vines refusing to set, his 
melons ^ shy-bearers.' Where seed is wanted, and little, and 
that perhaps of bad germinating power, is produced, the disap- 
pointment is naturally great. We are far from saying that the 
reasons for these untoward events can, in the present state of 
our knowledge, be at all times determined ; but we do say that 
the cause is often obvious, and that few more striking instances 
of the benefit which science may confer on practice can be 
adduced than those which vegetable physiology has conferred 
on the cultivator. 
We have seen that the structural changes affecting the repro- 
ductive organs of the flower may be reduced to — 1, an arrest ; and 
2, to exaltation ; or 3, to perversion of growth or of develop- 
ment. In seeking the causes of these changes it would seem, 
at first sight, natural to refer an arrested growth to a relatively 
deficient supply of nutriment, or to some other debilitating or 
obstructing cause. The opposite condition might as readily be 
accounted for by an increased food supply, or by the presence 
of other favourable conditions. No doubt this is true so far as 
it goes, but the problem is more complex than it appears to be 
on the surface. An arrest of growth, for instance, may arise 
from a superabundance of food, or from an inability to assimi- 
late it. One may starve in the midst of plenty. Again, it is 
notorious that exaltation of development, in one organ or set of 
organs, may be a sequela of impaired nutrition ; in others, the 
principle of compensation comes into play in such cases — if 
one part is debilitated, another takes on proportionately more 
vigorous development. If the balance be once disturbed, the 
opportunity for change is at once, and of necessity, afforded. 
To further illustrate this matter, we may now advert to the 
theory of Dr. E. Spruce ; and which, if not proved, at least 
affords a valuable focus for the concentration and correlation of 
evidence, and a good stand-point from which to discuss it. 
According to this theory the progenitor of existing plants had 
structurally and functionally hermaphrodite flowers. In course 
of time the economy of force accruing from division of labour 
led, and still leads, to a separation of the sexes. The health 
and vigour of the individual plant would be promoted by the 
separation, the number and vigour of its offspring increased. 
Once the equilibrium disturbed, natural selection would tend 
to perpetuate the change as one generally advantageous to the 
plant. The changes in question do not amount to the actual 
